Brightness of object is the intensity of light per solid angle per unit area, which is emitted or reflected by that object. A known problem in the art is how to improve the conditions where artificial light is added while capturing an image, e.g. when applying flash light under dark conditions, where the amount of ambient light present is not sufficient to obtain a good-quality image.
When capturing images (video and/or pictures) the process results in different apparent brightness of the objects included in the images, wherein the brightness differences are a function of the distance that extends from the object to the image capturing device, reflectivity of the object, amount of light incident on the object as well as its orientation relative to camera. As an example, flash photography often results in overly bright faces, which are much closer to the camera than the rest of the scene.
In order to somewhat reduce this problem, photographers have special dedicated equipment such as special flash devices, which are designed to scatter light upwardly, rather than directly onto the object. Other known solutions are the use of arrangements having large screens and reflectors.
Also, special techniques may be applied in order to reach an arrangement of objects which avoids high differences in object brightness.
U.S. Pat. No. 4,304,479 to Polaroid corporation discloses a photographic camera having either a built-in or detachably connectable electronic strobe light which provides a preferred illumination distribution over the field of view of the camera in order to maximize flash range and improve the quality of illumination for flash pictures. The strobe is provided with a reflector that is asymmetrically shaped about the horizontal plane having optical power which decreases at different rates about the horizontal plane. This arrangement provides a vertically asymmetric distribution of illumination over the picture area with the peak illumination occurring at the central upper part of the picture area. Side to side illumination of the picture is generally symmetric about the vertical axis and is controlled by a reflector and a cylindrical Fresnel lens. However, this device cannot be automatically adjusted based on detailed information on the target whose image is being captured.
U.S. Pat. No. 7,670,032 which acknowledges the importance of uniform illumination, teaches as a solution the use of a diffuser-reflector assembly for use with a photographic flash lamp which may be installed onto the light-emitting end of a flash lamp and adjusted per image setup. It may comprise specular or diffuse reflectors, color or neutral density filters, or a combination. The frames and inserts of the device may be swung on its arms and independently pivoted over a wide range of angles above the lamp, thereby providing a wide range of lighting effects. Still, as referred to in the previous solution above, this publication also does not teach in any way applying an automatic method for carrying out local adjustments based on the scene, and does not reach the local resolution required.
High-dynamic-range imaging (HDRI or HDR) is a technique used in imaging and photography to reproduce a greater dynamic range of luminosity than is possible while using standard digital imaging or photographic techniques. Thus, HDR imaging may be employed to improve the visibility of dark (far) objects and at the same time to prevent saturation of bright (close) objects.
HDR images can represent a greater range of luminance levels than can be achieved using more traditional methods, such as many real-world scenes containing very bright, direct sunlight to extreme shade, or very faint nebulae. This is often achieved by capturing and then combining several different narrower range exposures of the same subject matter. Non-HDR cameras take photographs with a limited exposure range, resulting in the loss of detail in highlights or shadows. The two primary types of HDR images are computer renderings and images resulting from merging multiple low-dynamic-range (LDR) or standard-dynamic-range (SDR) photographs. HDR images can also be acquired using special image sensors.
Due to the limitations of printing and display contrast, acquiring an HDR image is only part of the solution. One must also apply appropriate methods for displaying the results. The method of rendering an HDR image to a standard monitor or printing device is called tone mapping. This method reduces the overall contrast of an HDR image to facilitate display on devices or printouts with lower dynamic range.
The present invention provides a new solution that enables overcoming the problem described above.